1. Field of the Invention
The present invention relates to determination of the quantity of solar radiation of the sunlight coming into the passenger compartment of an automobile particularly when the azimuth of the sun is deviated from the direction of movement of the automobile. More particularly, the invention concerns a solar radiation quantity detecting device for use in an automobile air-conditioner.
2. Description of the Prior Art
There have been proposed control systems comprising a plurality of solar radiation sensors disposed on predetermined portions of the passenger compartment of an automobile, such as front and rear portions of the passenger compartment to be air-conditioned, for adequately controlling the air-conditioning of the front and rear portions depending on the detected signals from respective sensors. The proposed control system having such plural solar radiation sensors needs a number of electric wirings and hence a complicated signal processing system. With this difficulty in view, a simple control system is disclosed in Japanese Patent Laid-open Publication No. 62-73108, wherein a solar radiating condition detecting device composed of a plurality of solar radiation sensors is disposed on one portion of a passenger compartment. The disclosed solar radiating condition detecting device is aimed at an accurate detection of the current solar radiating condition and includes a solar radiating intensity and direction detecting unit composed of at least three solar radiation intensity detecting elements each for detecting the intensity of solar radiation impinging thereon and means for detecting the intensity and direction of solar radiation based on the intensity of solar radiation detected by each detecting element, and a solar radiating condition calculating unit for calculating the solar radiating condition of a selected portion of the passenger compartment based on the intensity and direction of solar radiation detected by the solar radiating intensity and direction detecting unit.
In this known control system, when the so-called "deviated solar radiation" exists, the quantity of solar radiation detected by the solar radiation sensors is considerably lowered under the influence of the windshield and the rear window of the automobile, in spite of the fact that the solar radiation quantity in this instance is substantially the same as the solar radiation quantity detected when the sunlight comes from the front of the automobile into the passenger compartment. Furthermore, the control system is unable to detect the solar radiation quantity when the sunlight comes rearward from the automobile. If the deviated solar radiation is corrected depending upon the detected solar radiation quantity, the amount of correction is smaller than should be performed in view of the actual solar radiation quantity. The term "deviated solar radiation" used herein is intended to refer to the condition where the direction of solar radiation, i.e. the azimuth of the sun is in the range of +60.degree.&lt;.alpha.&lt;+180.degree. and -60.degree.&lt;.alpha.&lt;-180.degree., for example.